This invention relates to an auxiliary box transmission control wherein a spring biases a piston in a first direction and a fluid cylinder biases the piston in a second direction.
Transmissions for heavy vehicles such as trucks typically include a main transmission box which can be utilized to select a plurality of speed ratios. The main transmission box then feeds into an auxiliary box. The auxiliary box typically provides a range and/or a splitter function. The range and splitter functions are provided by selecting one of two gear ratios. A fluid cylinder typically drives a piston to engage one of the two gears. Typically, solenoids and fluid controls are required for each side of the piston such that the piston can be driven in a selected direction to achieve a desired gear ratio in the auxiliary box.
It would be desirable to reduce and simplify the components in the auxiliary box.
In a disclosed embodiment of this invention, a fluid cylinder for driving a gear ratio selection member in an auxiliary box of a transmission is driven in a first direction by fluid pressure biasing a piston. A spring is compressed when the piston is driven in the first direction. If the fluid pressure is relieved, the spring drives the gear selection member in an opposed direction. In this way, the present invention simplifies the standard auxiliary boxes for transmissions by eliminating the requirement of an extra control valve and related fluid connections. The system ensures the auxiliary box is driven to a desired position by controlling the relative force between the fluid force and the spring force.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.